Centrifugal separator



1966 c. L. AMERO CENTRIFUGAL SEPARATOR Filed Feb. 5. 1965 United StatesPatent 3,228,594 CENTRIFUGAL SEPARATOR Clifford L. Amero, 17 WoodlandRoad, East Walpole, Mass.

Filed Feb. 5, 1965, Ser. No. 433,537 4 Claims. (Cl. 233-7) This is acontinuation-in-part of application Serial No. 154,752 filed Nov. 24,1961 and now abandoned. This invention relates to apparatus foreffecting separation of solids from liquids by centrifugal action andmore particularly to such apparatus wherein the solids-liquid slurry maybe subjected to chemical action while simultaneously undergoingcentrifugal separation, the chemical being such as to assist thecentrifugal force in producing separation of the solids.

With many slurries difficulty is experienced in obtaining satisfactorycentrifugal separations of solids from liquids, particularly where it isnecessary or desirable to remove very fine particles dispersed or incollodial suspension in the liquid phase or phases of the slurry. Formany such dispersions or suspensions there exist chemicals which willaid separation of such solids under normal gravitational settlingconditions, such as flocculants or coagulants or, in case the liquid isor includes an emulsion, in particular one stabilized by the presence ofsolids, individual chemicals or combinations of various chemicals knownas demulsifying agents which, through their specifics actions, promoteremoval of the particles and destruction of the emulsion. All suchchemicals are hereinafter referred to as flocculants.

In the past, efforts have been made to improve centrifugal separation byadding such flocculents to the slurry preliminary to feeding it to thecentrifuge. However satisfactory results have not been obtained in thatincreased solids recoveries have been so disappointingly low as to beuneconomical for most purposes. In consequence, it has been assumed thatflocculants act with very low efiiciency under the conditions involvedin centrifugal separation.

The object of this invention is to provide a centrifuge having novelcombination of structure for bringing flocculants together with theslurry and causing the same to act effectively to cause separation fromthe liquid of solids particles which are not separable therefrom bypractical centrifugal force levels alone, providing substantial andeconomical yields of such particles from the centrifuging operation.

The centrifuge according to this invention is of the socalled solid bowltype in which slurry is continuously fed into the rotating bowl and theclarified liquor or effluent thereof continuously overflows therefrom.Means are provided to form a shallow pool of slurry within the bowl, ofsmall depth compared to the bowl diameter, so that the differential incentrifugal force between the outer and inner faces of the pool is smalland the pool is subjected throughout its depth to substantially themaximum centrifugal force of the rotating bowl. This means that theagglomerates formed by chemical action are separated by centrifugalforce substantially as rapidly as they form and consequently before theyflow with the liquid to any substantial extent. This is an importantattribute, because I have found that chemically-induced agglomeratestend to redisperse under flow conditions, particularly if subjected toviolent agitation, and once this occurs the degraded agglomerates do notreform readily or substantially without additional chemical treatment.

Preferably, the centrifuge is also equipped with means for continuouslyremoving the separated solids from the bowl, this means taking the formof a conveyor coaxial with the bowl having helical blade or bladesdisposed in 'ating as a thin top layer on the bowl pool.

Patented Jan. 11, 1966 the pool and extending into the solids bed. Byrotating the conveyor in the same direction as the bowl but at a smalldifferential, a slow relative rotation of the bowl and conveyor isobtained, so that the solids may be continuously advanced to anddischarged from one end of the bowl. Due to its slow relative rotationthe conveyor does not agitate the slurry pool to cause turbulent flow,which would be adverse to effective chemical agglomeration. In additionto maintaining substantially constant liquidsolids conditions in thepool, the conveyor also acts to cause the liquid to flow in a spiralpath about the bowl axis. For purposes of the present invention, this isdesirable since it sub-divides the pool into one or more (depending uponthe number of blades in the conveyor) relatively narrow streams whichfacilitates certain applications of the chemical as hereinafterdescribed and, in addition, prevents any axial short-circuiting of flowwhich might tend to decrease the dwell of some of the liquid in thebowl.

In accordance with the invention, means are provided for feeding twodifferent flocculants to the slurry at two different locations spacedapart from each other. In many cases the first flocculant added producesby itself very little flocculation or agglomeration, but instead it maycondition the slurry so that it can be effectively acted upon by thesecond addition. In other cases the flocculant may be formed by theinteraction of the two separate chemicals with each other in thepresence of the slurry, as in the case, for example, with the use oflime and alum, in which case simultaneous addition of both chemicals atthe same location produces poor results. In such cases, one of thechemicals must be added to the slurry sufliciently in advance of theother so that it becomes uniformly distributed in the slurry before theaddition of the other.

The extent of spacing, both in terms of time and of distance, betweenthe two separate additions, may vary considerably depending upon theprecise nature of the slurry as well as upon the identity or nature ofthe chemicals added.

For best results, the second addition must be made to the pool withinthe bowl between adjacent turns of the conveyor blade. Liquids-solidsslurries are fractionated under centrifugal force so that the pool isactually formed of two or more layers of liquid-solids suspensions ofdifferent properties and consistencies, only one of which may containthe suspended solids fraction which needs chemical agglomeration to beextractable by centrifugal force. Chemical addition to the pool withinthe ma chine, therefore, desirably selectively treats only those solldsrequiring chemical agglomeration for settling. Some slurries contain anemulsion in which fine particles are suspended, this emulsion beinglighter than the remaining liquid-solids mixture of the slurry, andfraction- In such cases, it is advantageous to add the demulsifyingagent to the slurry in the pool and direct it to or into the particularlayer which the agent is designed specifically to treat.

Another important factor as regards the point or points of the secondchemical addition is that the dwell time of the liquid component towhich it is added in the bowl pool, after such addition, be sullicientto permit the chemical substantially to exhaust its treating power onthe materials on which it is intended to act and to give the treatedfractions the maximum dwell possible under centrifugal force. To thisend, I prefer to feed the slurry into the bowl adjacent the end oppositethe liquid discharge end so that the liquid component must flow forsubstantially the full length of the bowl before it is discharged,thereby providing a maximum dwell of liquid in the bowl. The secondaddition of chemical to the slurry is preferably made to the pool asclose as possible to the slurry feed point, so that a substantial dwelltime of chemically treated slurry in the bowl is available.

The point at which the first addition of flocculant to the slurry mustoccur is spaced from the second addition, as pointed out above, by anextent which depends upon the nature of the slurry and of theflocculant.. Where the flocculants are of such a type that a short timedelay only is neededbetween the first addition and the second, the firstaddition to the slurry may occur at a different point in the bowl pool,spaced from the first. If a somewhat longer time delay is required, thefirst addition to the. slurry may be made at or near its entrance intothe feed compartment. Where a still longer time delay between the firstand second additions and/ or a more thorough dispersion or interminglingof the first addition into the slurry is desired before the secondaddition is made, the first addition may be made to the feed slurryduring or in. advance of its entrance into the centrifuge, as forexample in the feed tank.

The machine of the invention includes separate feed lines connected orconnectable to different discharge locations so that selectively thesame chemical may be applied to the slurry at several points ordifferent chemicals or concentrations of a. chemical may be fed to theslurry at different points. Further, at least some of the dischargemeans are desirably adjustable so that their points of chemicaldischarge. to the slurry may be individually varied.

The foregoing and other features and advantages of the invention will bemore fully described with reference to the accompanying drawing, showingonly preferred embodiments, wherein:

FIG. 1 is a view partially in vertical longitudinal section, partiallyin side elevation, in part broken away, of a centrifugal separator andcertain auxiliary equipment according to the invention,.and

FIG. 2 is a fragmentary vertical longitudinal section view of amodification of the embodiment of FIG. 1.

Referring to FIG. 1, the centrifugal separator has a casing. Whichhouses the rotatingbowl and conveyor assembly of the machine. The bowl12 has fixed to its opposite ends hollow shafts 14 and 16 extendingrotatably through the opposite ends'of. casing 10 and supported insuitable bearing mounts (not shown) outside each end of the casing.Shaft 14 constitutes the drive shaft for the. assembly and has fixed toits outer end a belt drive sheave .18 by which the assembly may berotated from a suitable power source (not. shown). Shaft 16 is connectedat its outer end to a reduction gear unit 20 through which, in wellknown manner, the rotation of shaft 16 causes'rotation in the samedirection at a slight speed differential of a shaft 22 rotatablyjournaled within shaft 16 and coaxial therewith. Shaft 22 is fixed tothe corresponding end of conveyor24, the opposite end of which has ahollow shaft 26 rotatably journaled within bowl drive shaft 14. 7

As shown, conveyor 24 is formed of a cylindrical hollow casing 28 to theopposite ends of which the shafts 22 and 26 are secured and to theperiphery of which is secured one or more (one being shown) conveyorblade 30, projecting therefrom to adjacent the inner surface of thebowl. Blade 30 is so directed and pitched as to convey the solidsdeposited on the inner surface of the bowl to the solids discharge end,which is the right-hand, end of the embodiment illustrated in FIG. 1.

Bowl 12 may have various shapes but as shown has a cylindrical. sectionand a frusto-conical section, the latter section being located at, anddiminishing in diameter toward, the solids discharge end. Conveyor blade30 is dimensioned to conform to the bowl shape and so as normally toprovide a substantially uniform clearance from the inner surface of thebowl. A ring 32 projects radially from the outer surface of the bowladjacent the solids discharge end and to, this ringis secured theannular base of a spider 34 which is'fixedly connected to the driveshaft 14. A ring 36 projecting inwardly from casing 10 and closelyclearing the base of spider 34 forms with the adjacent end wall ofcasing 10 a solids discharge compartment 38 into which the solids areprogressively dis charged by the action of the conveyor, through theadjacent open end of the bowl and between the arms of spider 34.Impeller blades 49 mounted on a portion of conveyor hub 28 projectingbeyond the solids discharge end of the bowl, and having their inneredges close to this bowl end, facilitate solids discharge intocompartment 38. Solids are continuously discharged from compart ment 38through an outlet (not shown) in the base thereof.

At the opposite end of the bowl, an outwardly pro jecting annulus 42 hassecured thereto an end closure plate 44'which is provided with'aperturesin the form of slots 45. Weirs 46 are adjustably mounted on plate 44 sothat they may be adjusted toward and away from the bowl axis to formadjustable dams over which the efiluent must flow in escaping from thebowl through slots 45, and thus defining the depth of the poolmaintained in the bowl.

Within the hollow casing 28 of the conveyor, a transverse wall 48adjacent the solids discharge end of the bowl defines one end of aslurry feed compartment, the opposite end of which is closed by a flangeon shaft 26 and 'a cooperating inwardly projecting ring on the conveyorcasing to which it is attached. A stationary slurry feed pipe 50 extendsaxiallythrough the hollow core of conveyor shaft 26, said shaft beingrotatable about pipe 50. Pipe 50 is provided adjacent its inner end withan outlet opening 52 into the feed compartment and at its other end isconnected by T connection 54 and. pipe 56 with a suitably regulatedsource of constant slurry flow (not shown). The slurry discharged intothe feed compartment receives there its initial acceleration toward theultimate rotaryspeed of the bowl, to which the slurry is discharged fromthe feed compartment through outlet 7 openings 58in the wall of casing28.

A first chemical feed pipe 60 extends through slurry feed pipe 50 andhas its inner end turned downwardly to discharge into the core of theslurry stream. passing into the feed compartment through the outlet 52.Pipe 68 is connected to a first chemical supply tank 62 through a flowregulator 64 and a flow control valve 66. A second chemical feed pipe 68also extends through the slurry feed pipe 50 and has its inner dischargeend extending through the closed end wall of feed pipe 50 and alsothrough wall 48 into a compartment in casing 28 of conveyor 24 formedbetween wall 48 and a second transverse wall 70 in casing 28. Pipe 68 isconnected .to a second chemical supply tank 71 through flow regulator 72and flow control valve 74 .and intermediate piping.

Nozzles 76, 78 are arranged to discharge chemical from between the walls70 and 48 to the bowl pool. Preferably, they are adjustable in length,for example, being exteriorly threaded and received through threadedbushings in the casing 28 so that they may be selectively positionedwith their outlet ends located beneath the inner surface of the bowlpool (indicated by the dotted line P in FIG. 1), as in the case ofnozzle 76, or they may have their outlet end located above the poolsurface, as in the case of nozzle 78. It will be appreciated that wall48 rotates around stationary feed pipe 68. As shown, clearance isprovided between the wall and the pipe for this purpose as there islittle likelihood of leakage between the slurry and chemical feedcompartments, but, if desired, Wall 48may be connected to pipe 68through a rotary seal.

The arrangement shown permits feeding of flocculant to the slurry bothas it enters the slurry feed compartment and after it has entered thebowl pool. More or less than the two nozzles 76, 78 shown may beprovided for discharging flocculant from the flocculant feedcompartment, and they all may be adjusted to discharge the chemicalbelow or above the inner surface P of the pool. Flocculants that aredifferent either in nature or in concentration may be supplied throughthe two pipes.

Flocculant supplied through the pipe 60 is thoroughly intermixed withthe slurry by the agitation produced as the slurry is accelerated towardthe rotational speed of the bowl in the slurry feed compartment anddischarged through the openings 58 to the bowl pool. The agitationinvolved in this acceleration is completed before the chemical has timeto act on the slurry and therefore does not interfere with itsoperation. After the chemically treated slurry enters the bowl pool itremains in a relatively quiescent condition, flowing smoothly in thehelical course provided between conveyor blades 30 toward the left handend of the bowl as shown in FIG. 1, where it is discharged over dams 46into an effluent discharge compartment 80 formed between the end wall ofmachine casing and the end of the rotating bowl and conveyor assembly.The efiiuent is continuously withdrawn from the bottom of compartment 80through a suitable outlet (not shown). Thus, the chemical appliedthrough pipe 60 acts on the slurry throughout its period of dwell in thepool and while it is in a relatively quiescent state, as is ideal forits effective action. It will be noted that the slurry feed is locatedat the maximum practical distance from the liquid discharge end of thebowl. This is desirable since it forces the slurry liquid to travel thefull length of the bowl before discharging as efiluent, and also insuresthat all of the slurry liquid will flow past any point of chemicaladdition to the pool.

Particularly where the flocculant is lighter than the slurry and tendsto concentrate at the inner surface of the pool, or where a light liquidphase tends to fractionate to the inner surface of the pool, it may bedesirable to provide means for insuring a thorough mixing of flocculantswith the slurry in the pool. To this end, there may be provided one ormore (one shown) annular bafiie 82 attached to and surrounding conveyorcasing 28 between turns of blade 30, the baffle extending in a planesubstantially normal to the bowl axis below the surface of the liquid.In order to reach the effluent discharge end of the pool, the slurryliquid must pass from one side to the other of the bafiie and thereforemust pass under it, with a tendency for the top layer of the pool to mixwith underlying portions.

In certain cases it may be desirable to supply chemical from one of thesupply tanks only to both feed pipes 60 and 68, or to switch either orboth tanks from one feed pipe to the other. To this end,cross-connecting pipes 84, 86 may be provided connected at one end tocontrol valves 66 or 74 and at the other end to the other pipe 60 or 68.In such case, valves 66 and 74 are adapted to switch all or part of theflow to pipe 84 or 86 and thereby to the other feed pipe 60 or 68.

FIG. 2 is a fragmentary view of apparatus similar to that of FIG. 1 butillustrating a modification, parts which are the same in the two figuresbeing designated by primes of their reference numerals in FIG. 1. In theFIG. 2 modification, a third chemical feed pipe 90 is provided extendingthrough slurry feed pipe 50' and may have its outer end connected to athird source of chemical (not shown) which may be similar to the sourcetanks and connections shown in FIG. 1. A third wall 92 within theconveyor casing 28' and inclined to the axis thereof forms two chemicalreceiving compartments between wall 92 and walls 48 and 70 respectively.Feed pipes 90 and 68' extend through wall 48 (which is rotatable withrespect thereto), pipe 90 terminating in an outlet between walls 48 and92. Pipe 68 extends through wall 92 (which is also rotatable withrespect thereto), with its outlet located between walls 70' and 92. Thenozzle or nozzles 7 6' discharge into the pool the chemical fed frompipe 68 and the nozzle or nozzles 78' discharge to the pool the chemicalfed from pipe 90. Pipe 60 is available to discharge chemical into theslurry entering the slurry feed compartment, as in FIG. 1 embodiment.Wall 92 is inclined to the bowl axis to provide in each chemical feedcompartment a maximum of conveyor casing wall space between helicalturns of blade 30' in which nozzles may be inserted if more than one ineach compartment is desired.

The arrangement of FIG. 2 make it possible to feed two differentflocculants to the bowl pool separately and simultaneously at differentpoints in the direction of liquid flow. By employing both pipes 68 andthere is provided a minimal separation between the two additions,different adjustments of the two nozzles 76', 78 making it possible tofeed two chemicals to the slurry pool at different distances from thebowl axis. Thus, as shown, the nozzle or nozzles 76 may discharge belowthe pool surface and the nozzle or nozzles 78 at or above the poolsurface. In the case of slurries which tend to fractionate in the poolinto layers of distinct solids-liquids compositions for which differentchemical treatments are desirable, this arrangement permits such layersto be separately treated with the desired chemicals.

While there will be in general at least two feed pipes dischargingseparately to the slurry and connectable to two different chemicalsources, it will be appreciated that three or more may be usedsimultaneously, depending on the nature of the slurry to be treated.Multiple feed pipes may, of course, be arranged coaxially rather thanside by side as shown.

It should be understood that in the foregoing description of theinvention, I have used the term fiocculant, as referring to any fluidwhich has, or which contains any material which has, when mixed with aliquid-solids slurry, a beneficial effect onseparation by centrifugalforce of at least a portion of the solids content from the slurry. Suchtreating agents may act by flocculating, coagulating or sequestering theindividual solid particles into agglomerates which are more subject toseparation by centrifugal force. They may also act by breaking anemulsion or complex in which the particles are bound, or in other ways.They may or may not be beneficial to separation of solids from theparticular slurry concerned under ordinary gravitational settlingconditions.

By means of the apparatus of the present invention, I have found itpossible to treat slurries of various types with appropriate suchflocculants to produce substantial increases in solids recovery whichare not obtainable by adding the same agent or agents, even in greaterquantity, to the slurry in the feed tank preliminary to feeding it tothe centrifuge. Slurries so successfully treated have included simplewater-solids mixtures such as aqueous suspensions of fine clay particlesand more complex slurries such as digested sewage sludge and oil-wateremulsions from refinery waste containing suspended fine solid particles.

The diameter of the bowl and the speed at which it is rotated may varywidely, depending upon the nature of the slurry, the capacity needed andthe amount of centrifugal force required. In general, in order to insuremaximum separation they should be such as to produce high centrifugalforce on the pool, of the order of up to 3,000 X gravity or more.

It should be appreciated that I have described and illustrated on'lypreferred embodiments of the invention and that various changes may bemade in details thereof without departing from the spirit and scope ofthe invention.

I claim:

1. Apparatus for separating solid particles from liquid which includes arotatable solid bowl adapted to receive a stream of the fluid-solidsslurry to be separated, said bowl having end outlets for discharging theliquid and solid fraction separately therefrom, said liquid fractionoutlet being positioned to maintain an annular pool of slurry within thebowl of a depth which is a small fraction of the bowl diameter, saidpool extending substantially the full length of the bowl, a conveyorrotatably, co-' axially mounted within the bowl and having a blade extending helical'ly of the bowl axis and projecting into said pool, meansconnected to the bowl and conveyor for rotating the same at a smalldifferential speed in the same direction such as to maintainv said poolunder high centrifugal force, so that solids of said slurry areconcentrated against the bowl and are progressed to said solidsdischarge outlet by said conveyor blade, and flocculant feed meansassociated with said slurry supply means for adding fiocculant to saidslurry, including two supply tanks each containing a differentflocculant, and separate feed lines to feed flocculant from each tank tosaid slurry before the slurry has been subjected to substantialcentrifugal action in said bowl, at least one of said feed linesextending into said bowl to discharge flocculant to said slurry poolbetween adjacent turns of said conveyor blade, and the other of saidfeed lines having its inlet positioned to discharge flocculant to saidslurry in advance of said said one feed line.

2. Apparatus as claimed in claim 1 wherein one of said flocculant feedlines includes nozzle means extending into said pool for discharging theflocculant below the pool surface.

3, Apparatus as claimed in claim 1 wherein said floc- 8;: culant feedlines each include a compartment in said conveyor, each compartmentseparated from the other, and nozzle means for discharging fiocculantfrom each of said two compartments, one of said nozzle means having itsoutlet disposed above, and the other having its outlet disposed below,the surface of said slurry pool.

4. Apparatus as claimed in claim 1 in which said slurry supply meansincludes a compartment within said conveyor through which the slurrystream is fed and in which the slurry is initially accelerated to arotary speed approching that of the bowl, and one of said flocculantfeed lines discharges into said slurry stream as it reaches saidcompartment.

References Cited by the Examiner UNITED STATES PATENTS 2,308,559 1/1943Winkler 2337 X 2,685,369 8/1954 Crossley 233-14 X 2,867,582 1/1959Shuman et al. 3,096,282 7/1963 Trotter 233--7 M. CARY NELSON, PrimaryExaminer. H. KLINKSIEK, Assistant Examiner.

1. APPARATUS FOR SEPARATING SOLID PARTICLES FROM LIQUID WHICH INCLUDES AROTATABLE SOLID BOWL ADAPTED TO RECEIVE A STREAM OF THE FLUID-SOLIDSSLURRY TO BE SEPARATED, SAID BOWL HAVING END OUTLETS FOR DISCHARGING THELIQUID AND SOLID FRACTION SEPARATELY THEREFROM, SAID LIQUID FRACTIONOUTLET BEING POSITIONED TO MAINTAIN AN ANNULAR POOL OF SLURRY WITHIN THEBOWL OF A DEPTH WHICH IS A SMALL FRACTION OF THE BOWL DIAMETER, SAIDPOOL EXTENDING SUBSTANTIALLY THE FULL LENGTH OF THE BOWL, A CONVEYORROTATABLY, COAXIALLY MOUNTED WITHIN THE BOWL AND HAVING A BLADEEXTENDING HELICALLY OF THE BOWL AXIS AND PROJECTING INTO SAID POOL,MEANS CONNECTED TO THE BOWL AND CONVEYOR FOR ROTATING THE SAME AT ASMALL DIFFERENTIAL SPEED IN THE SAME DIRECTION SUCH AS TO MAINTAIN SAIDPOOL UNDER HIGH CENTRIFUGAL FORCE, SO THAT SOLIDS OF SAID SLURRY ARECONCEN-